This invention relates to novel uses of a material known as “coal combustion residual” (“CCR”). CCR is finely comminuted particles of material that remain after coal has been burned to provide the immense quantities of heat required to operate high-pressure steam boilers in coal-fired electric power plants operated by electric power utilities such as the Tennessee Valley Authority, Duke Energy and others. CCR accumulates in vast quantities, and storing the material requires expense and creates environmental risk. In recent years, regulatory authorities have taken an increasingly negative view of the manner in which CCR's are stored and have enacted regulations that will require that CCR's be handled in a manner different from past practice.
CCR include fly ash, bottom ash, boiler slag, flue gas desulfurized gypsum (FGD Gypsum) and coal combustion products.
The management of CCR is regulated at both the federal and the state level. The Federal CCR Rule, 80 Fed. Reg. § 21302 (Apr. 17, 2015) and the Direct Final Rule (Oct. 4, 2016), regulate coal ash as a solid waste and not as a hazardous waste. The Rule sets minimum standards for disposal and/or disposition of coal ash. Other state and federal regulations continue to apply to CCR disposal. The Federal CCR Rule includes detailed standards for the design and location of CCR landfills and impoundments, groundwater monitoring, remediation, structural integrity and final closure of landfills and impoundments.
The Federal CCR Rule does not regulate practices that meet the definition of a “beneficial” use of CCR, which must meet all of the following conditions, as found in 80 Fed. Reg. at § 21349:                (1) the CCR must provide a functional benefit;        (2) the CCR must substitute for the use of a virgin material, conserving natural resources that would otherwise need to be obtained through practices such as extraction;        (3) the use of CCR must meet relevant product specifications, regulatory standards or design standards when available and when such standards are not available, CCR are not used in excess quantities; and        (4) when un-encapsulated use of CCR involves placement on the land of 12,400 tons or more in non-roadway applications, the user must demonstrate and keep records and provide such documentation upon request, that environmental releases to groundwater, surface water, soil and air are comparable to or lower than those from analogous products made without CCR, or that environmental releases to groundwater, surface water, soil and air will be at or below relevant regulatory and health-based benchmarks for human and ecological receptors during use. EPA's final CCR management rule (https://www.regulations.gov/doucment?D=EPA-HQ-RCRA-2009-0640-11970), and EPA's direct final CCR management rule https://www.epa.gov/coalash/coal-ash-rule. Worldwide web links are provided for easy reference.        
Any use that fails to comply with each of the above criteria is considered “disposal” of CCR and is subject to all disposal requirements in the Federal CCR Rule.
More specifically, the present invention relates to utilization and construction of containment structures and mine reclamation projects using specialty design mixes made from encapsulated CCRs and other industrial byproduct materials. The mix designs described in this application have application in load bearing, improved/encapsulation, roller-compacted concrete (RCC) and the carbon capture flowable fill materials. All of the mix designs have been developed so that the US EPA guidelines for beneficial use of industrial non-hazardous materials are achieved or exceeded. In addition, to mix designs that safely and effectively contain potential contaminants in CCRs and other industrial byproduct materials, this invention provides guidelines for ensuring beneficial use through encapsulation and mitigation of the leaching potential of harmful contaminants. This is accomplished by following the Final CCR Rule, Apr. 17, 2015, and the US EPA Methodology for Evaluating Beneficial Uses of Industrial Non-Hazardous Secondary Materials, April 2016 [2, 3] and applicable standard guides from American Society of Test Materials E-50 Committee. This invention achieves the four criteria for beneficial use as defined by the US EPA: (1) The CCR must provide a functional benefit; (2) The CCR must substitute for the use of a virgin material, conserving natural resources that would otherwise need to be obtained through practices such as extraction; (3) the use of CCR must meet relevant product specifications, regulatory standards or design standards when available, and when such standards are not available, CCR is not used in excess quantities; and (4) the proposed application is an encapsulated use of CCR as defined by the US EPA Final CCR Rule.
In order to achieve suitable encapsulation of CCRs and other deleterious materials, the mix design and applications for this invention follows the required US EPA requirements. Specifically encapsulated beneficial uses are those where the material is bound in a solid matrix that minimizes mobilization of heavy metals and other deleterious constituents into the surrounding environment. Examples of encapsulated uses include, but are not limited to: aggregate in concrete; a replacement for or raw material used in production of, cementitious components in concrete or bricks; filler in plastics, rubber and similar products; and raw material in the manufacture of a product such as wallboard.
One of the key aspects of this invention is the practical application of US EPA methodologies for verifying protection of the environment and the required characteristics to qualify as a beneficial use as defined by the US EPA Final CCR Rule. Following this Rule, will pre-qualify or pre-screen the uses identified in this patent by identifying the limiting factors that would influence the scoping, siting and impact analysis for the CCR material or site under consideration. This is accomplished by pre-testing (i.e. using the LEAF test methods of SW-846) the CCR material so that the leaching characteristics are controlled or mitigated. This pre-project testing and evaluation for this invention is expected to include:                (1) verification that deleterious substances and/or metals in the materials are bound in a solid material or solid-like material;        (2) site-specific scoping and site selection is appropriate from the US EPA impact analysis perspective, and        (3) offering guidelines for site characterization that are consistent with approved US EPA methodologies such that mobilization of deleterious constituents to the surrounding environment is controlled and/or eliminated.        
Since mortar materials used in load bearing walls, RCC dams and mine reclamation projects can require the use of aggregates to obtain sufficient strength, this invention includes and incorporates the use of fine sand and coarse aggregates developed from CCR, and other industrial byproducts, or commercially available aggregates. The invention includes offering design guidelines and installation methods so that the aggregates, products and containment structures are considered encapsulated products either by pre-testing or by following US EPA methodologies. This method includes developing mix designs that achieve the three primary characteristics of strength, durability, and reduced permeability and leaching potential.
The design features for this invention are unique because they will be tested and applied not only for resistance to weathering and providing adequate strength, but also for protection of the environment. This application of the principle of durability is outlined in documents provided by the US EPA on the use and application of the LEAF protocol for site assessment, evaluation of materials and design. In addition to strength, the materials in the mix designs for this invention will minimize or prevent the leaching and migration of deleterious constituents from the CCRs and/or industrial byproduct materials into the surrounding environment.
The invention recognizes that pre-existing patents may exist for lightweight aggregates and other application of CCR materials in the fields of road, dam and building construction. The disclosure of this application provides an integrated approach that utilizes existing technology and industry-recognized methods in novel ways for improving concrete material to maximize the beneficial use of CCR and other industrial byproduct materials while providing an innovative approach for the use of CCR materials.
Each year in the United States over one hundred million tons of coal combustion ash is generated and must be used or disposed of in some manner. Approximately half of the ash is now disposed of by on-site landfilling. However, some small part of the ash is used as a component in building materials mainly cast-in-place concrete or concrete pavement roadways. (See American Coal Ash Association (ACAA) Coal Combustion Product (CCP) Production & Use Survey Report, 2013 and 2015)
Other potential uses for fly ash and other CCRs have been surveyed by the ACAA and include structural fills, roadway embankments, mine reclamation, underground mine backfilling, and as a cement replacement—concrete, agriculture uses, and many others. The physical and chemical composition and characteristics of coal combustion fly and other CCRs can vary depending upon the type of coal that is burned and the type of combustion equipment and the conditions of combustion. The most common types of coal ash are class F fly-ash (ASTM C-618-15, Class F; finely divided residue produced from burning anthracite or bituminous coal); fluidized bed combustion (FBC) ash (produced from burning coal with limestone in a fluidized bed combustion furnace); and class C fly ash ASTM Designation No. C618-15, a finely divided residue produced from burning lignite or sub-bituminous coal and having a lime content that is typically higher than 10%). More complete descriptions of the types, properties and composition of various types of coal combustion ash have been provided in, for example, Material and Research Society Proceedings, Volumes 43, 113, 136 and 178.
One use of CCR disclosed in this application is for load-bearing walls, and walls made from mortar mixes with a high CCR content. Load-bearing walls and concrete members are proposed utilizing general guidelines established in technical articles by Ohio State University, the US Bureau of Reclamation for RCC Dams, and the National Precast Concrete Association. Elevated percentages of coal fly ash as a cement replacement is known to increase the workability, decrease the water/cement ratio, and increase durability of the concrete mix (Coal Combustion Products Utilization Handbook, WE Energies, 2013). Typical percentages of Type F or Type C coal fly ash as a portion of the cement range from 15 to 30 percent for moderate replacement and 30 to 50 percent for high replacement in precast structures. For cast in place load bearing walls, the CCR or fly ash replacement percentage can be increased to 50 to 70 percent depending on the requirements for early strength of the concrete or mortar mix and the need to control cracking caused by hydration of the Cementous materials.
The compressive strength of the different mix designs utilizing fly ash range from 3,000 to 4,000 psi for load bearing walls depending on the percentages of aggregate, fly ash, water and cement that are used. As disclosed in this application, the percentage of CCR content for load bearing walls would be dependent on the thickness of the load bearing wall, the surcharge load applied to the wall and the width and length of the bearing surface of pre-cast concrete members. Some embedment of steel and/or a special keyway locking structure may be required depending on the lateral forces developed from the geotechnical global slope stability evaluation. These products and methods relating to load bearing structures will require verification that the mix design, structural design, and site-specific application will be required to meet the three primary performance criteria of strength, durability and reduction in permeability/leaching potential.
Another proposed use of CCR's as disclosed allows the use of CCRs as the main component RCC dams for containment of compacted CCRs and/or as the buttress for a large CCR structural fill project.
The United States Bureau of Reclamation (USBR) Manual entitled “Roller-Compacted Concrete Design and Construction Considerations for Hydraulic Structures, 2005” indicates an acceptable percentage of coal fly ash and other CCRs for this type of application as high as 50 to 70 percent. The elevated percentage of CCRs as compared to Portland cement is possible because the CCRs serve as both a cement material replacement and a fine aggregate material. A higher percentage of fly ash can result in reduced strength. Accordingly, a limiting factor may be the load bearing capabilities of the CCR and RCC structure when evaluated using conventional geotechnical design and slope stability evaluation methods.
When this invention or method is used as an RCC containment wall that supports water and/or a surcharge load of fly ash or backfill material, a complete geotechnical investigation including and foundation design and global slope stability analysis will need to be conducted so that the RCC design and site-specific-application will meet the three primary performance criteria of strength, durability and reduction in permeability/leaching potential.
A third application according to the disclosure of this application includes the use of encapsulated CCRs in a specialty mix design that can function as the aggregate and Cementous component for the construction of a stable mine reclamation material. The use of CCRs in mine reclamation has been well documented in design guidelines and numerous case studies by State agencies and the US Office of Surface Mining Reclamation and Enforcement (OSMRE). This method will address many of the concerns and consideration in previous OSMRE documents by pre-testing and pre-design to verify strength, durability and reduction in permeability and leaching potential of deleterious constituents from CCRs.
The dual purpose of the encapsulated flowable fill material made of CCRs with a predetermined percentage of cement and/or lime and specialty additives enables the material to be used to:                (1) reclaim mine with a mix that provides adequate strength to support unstable areas;        (2) provide a balanced mix that has suitable flow characteristics for top down or injection installation to bridge unstable areas of the mine while maintaining sufficient durability to reduce the potential for acid mine drainage;        (3) has a low enough permeability to provide reduced leaching potential and to contain deleterious constituents in the solidified, encapsulated mix, and        (4) if required to provide a sufficient open-graded or air entrained cementitious material that is a stable matrix for carbon capture.        
Typical percentages of coal fly ash and other CCRs for the mine reclamation application would range from 70 to 90 percent depending on the pozzolanic activity of the coal fly ash and design requirement for the mine reclamation. When a method according to this disclosure is used for above ground or below ground mine reclamation, the mix design and site-specific methods will be required to address applicable State mine reclamation guidelines and the requirements of the Surface Mining Control And Reclamation Act of 1977.
The novel approach of this invention is to create contaminant structures to create a renewable energy storage area while providing remediation of an industrial material that is required to meet strict regulatory requirements.
The mix designs for the three uses outlined above involve high replacement percentages of cement with CCRs, and a reduction in the amount of water required by increasing the percentage of coal fly ash and other CCRs that are utilized. The use of coal fly ash in concrete and mortar mix designs is an established and effective approach that is been well understood for many years and documented in numerous industry papers. Recent developments using very high percentages of coal fly ash and other CCRs in concrete and mortar mix design have indicated that strength is increased and workability is improved with increasing amounts of coal fly ash to reduce the required amount of manufactured Portland cement. The amount of coal fly ash used in a mix design is dependent on the strength and workability requirements that must be tested on a project and site-specific basis.
Containing and/or encapsulating heavy metals and other deleterious constituents in structures or materials a component of the novel approach of this invention is recommended by the US EPA when structures with high percentages CCRs or coal fly ash are applied in the natural environment. The leaching potential of heavy metals from concrete and/or Cementous structures are best measured by performing a series of leaching potential tests according to the Leaching Environmental Assessment Framework (LEAF) developed by Vanderbilt University for the US EPA. For purposes of this invention, the concrete or mortar mix designs will be developed to provide adequate containment as determined by an acceptable reduction in the leaching potential of heavy metals as determined by the LEAF protocol and applicable sections of US EPA SW-846.
For development of this invention and its application in loading bearing walls or structures, the following mix design parameters are provided using the design principles from the US Bureau of Reclamation, Ohio State University. The mix designs for this invention are unique because they achieve a balance of the three primary characteristics of strength, durability and reduced permeability/leaching potential.
The use of coal fly ash and other CCRs in the concrete mix is designed achieve strength, workability, durability, reduction in permeability and containment of CCRs to provide an energy storage system. The United States Bureau of Reclamation (USBR) has developed guidelines for the use of coal fly ash in RCC dams and the process for optimizing the percentage of coal fly ash in RCC mix designs. Notable case studies by the USBR at the Upper Stillwater Dam, in 1987 indicated high durability, low permeability RCC mix design using fly ash to cement replacement percentage as high as 68 percent. The USBR Manual Roller Compacted Concrete Design and Construction Considerations for Hydraulic Structures provides guidelines for developing RCC mix proportions that optimize the use of coal fly and performance of the structures based on:
(a) compressive strength and elastic properties,
(b) cement plus pozzolan content and cement to pozzolan ratio,
(c) thermal properties; and
(d) durability.
With regard to the use of RCC dam mix designs for this invention, the novel approach includes optimizing the mix design to provide containment, encapsulation and prevention of leaching of heavy metals and other deleterious constituents to the natural environment. For the RCC dam mix design used by this invention, determining the durability and leaching potential of the aggregate used in the RCC dam containment structure will also be required. This will be accomplished by testing hardened specimens of the RCC mix for leaching potential and raising or lowering the amount of coal fly ash and cement content to achieve a mix that has the required compressive strength and reduction in the leaching potential of heavy metals and other deleterious constituents to the natural environment. The RCC mix design for this invention is unique because it achieves a balance of the three primary characteristics of strength, durability and reduced permeability/leaching potential.
Because the quality of the fly ash can vary depending location and method of combustion, the strength, durability and reduced permeability of the mix designs will be verified by testing prior to final design or application. Since the construction of RCC dam structures for containment of water and CCR requires development and use of quality control procedures in the field, application of the novel features of this disclosure will also include development and use of mix designs that utilize hydrophobic chemicals such as organosilanes and other permeability reducing additives. The use and optimization of these materials and additives for controlling leaching potential from CCRs and coal fly ash materials used in structural fills and mine reclamation has been established by previous research. “Preserving Structural Fill and Mine Reclamation as Acceptable Beneficial Reuse of CCRs”, Hardin and Daniels, 2011. Recognizing that the Cementous qualities of coal fly ash and other CCRs vary, will require that project specific RCC mix designs be developed for optimize strength and ensure adequate containment of heavy metals and other deleterious constituents. The following tables from USBR literature are incorporated as part of the technical basis for RCC dam mix designs for this invention. It is recognized that additional testing will be required to provide the combination of strength, durability and reduction in leaching potential that is one of the novel components of this invention.
The State of Pennsylvania from 1970 to 2000 implemented several innovative mine reclamation projects that utilized a wide variety of coal ash and other industrial byproducts. Since 1982, the Pennsylvania Department of Environmental Protection (PADEP) has administered an extensive coal mine reclamation plan that has provided guidelines for mine stabilization using fly ash stabilized with cement, lime and a variety of industrial byproduct materials. Many of these guidelines are available through the U.S. Office of Surface Mining Reclamation and Enforcement (OSMRE). The focus of many of these guidelines is to safely stabilize a coal mine with flowable mix designs that can be placed from the surface.
This invention provides a coordinated use of the mine reclamation mix designs available from the OSMRE in conjunction with improvement measures that create some porosity, while maintaining adequate long-term stability and encapsulation. This is accomplished by utilizing chemical additives that work with the inherent properties of coal fly ash, while maintaining the Cementous and pozzolanic properties of cement. This invention will require testing and validation of mine reclamation stabilization (OSMRE methods), carbon absorption potential (CREAT system, patented by Dr. S. Chen in China), and the encapsulation as measured by the US EPA Leachability Environmental Assessment Framework (LEAF) protocol. The test methods developed as part of the CREAT system are already being used effectively in other parts of the world, and this invention will allow application of these methods for carbon capture utilizing large volumes of CCRs in a manner that meets the requirements of the US EPA. The mix design for this invention is unique because it achieves a balance of the three primary characteristics of strength, durability and reduced permeability/leaching potential.
The properties necessary to cost-effectively stabilize coal mines, absorb CO2 and encapsulated metals are all enhanced by a mix of fly ash, lime and/or cement. The percentages of each additive depend on the unique properties of the coal fly ash and the site-specific characteristics present at the mine that is reclaimed. This invention utilizes existing technologies with an optimized or specially designed mix of fly and cement to create the required performance. The US EPA Methodology for Evaluating Beneficial Uses of Industrial Non-Hazardous Secondary Materials, April 2016, provides a framework for applying these technologies in a manner that enhances environmental protection and ensures beneficial use of industrial byproduct materials.